Subject: Extended PSRU
From: ACRE
Date: 7/16/2003, 6:51 PM


Proper design takes all modes of operation into consideration.
Just before an airplane takes off, and this applies to any airplane,
a rotation to near max angle of attack occurs (just short of stall).
If the angle of attack of the wings sitting on the gear is
negative all the speed in the world will not get you
off the ground. Same goes for a too high thrust line.
Any airplane must be able to rotate to near max
angle of attack when the lift available at that angle of
attack and speed equals the weight of the airplane.

Rutan limited the control authority of the canard to prevent
stall of the main wing. This means the canard also has a limited
ability to rotate the air plane at what should be the take off speed.

There fore the way to fix this is lengthen the nose gear and
increase the angle of attack of the canard and the main wing
while the airplane is sitting on the ground. The canard, being
well ahead of the main wheels, will have a larger positive moment
to overcome the negative moment caused by the high thrust line.

Takeoff distance will be shortened and the airplane will not jump
off the ground when the thrust is reduced as you claim happens.

On landing leave the nose gear strut as short as it is now.

The Germans fixed the ME262 take off problem by going to tricycle gear
thereby raising the tail.

Paul Lamar




Joseph Berki wrote:




 If you make the fuselage deeper the  thrust line stays the same with
 relation to flying surfaces while the  prop gets more ground
 clearance.  This will permit moving the prop aft or swinging a bigger
 prop.  The nose gear must be longer but the forward pivot point could be
 move forward to accommodate the additional length.

 Joe Berki
 Limo EZ




Good idea Joe.

Paul Lamar




Paul, Next time you get in the 182 and you start through the checklist, stop and think when you come to the line that says
"trim
set in take off position". Is the fact that the trim must be set for this high power condition a design defect? You guys
that
fly these not Wright aeroplanes just don't get it. That's the elevator out there where God and the Brothers meant for it to
be
and it operates in a superior fashion to that bass ackward thing from the Cesspool, but it still requires trimming for power
changes. ;-)

Rick


No.. no Rick you got it wrong. Cessnas have effective flaps that lower the landing
and crash speeds as God and Cessna intended. That is the reason for the trim.

You can't put flaps on a canard main wing as there is no, non, nada  pitch authority.

Paul Lamar


Paul, Rubbish, angle of attack is directly related to power setting with or without flaps. Change the power setting, trim out
the stick forces for that angle of attack. What the heck kind of instructors do they have down in the Granola State that they
don't teach you that?

Rick

Yes there is a minor effect of power but the major effect is the presents or absence 
of flap deployment. The forces involved are an order of magnitude greater as the 
center of lift drastically moves aft with the deployment of Fowler flaps.
Ask anybody that has flown a 182.

Anyway we are diverging from the fundamental problem and that is the blanking
of the prop by the pusher cowl. Our goal is to move the prop aft and/or up
and deal with the resulting problems. If you move it up and pitch change is
a problem with the application of power and since the canard does not have 
enough authority to deal with it you can reduce the lift on the main wing 
by raising the flaperons :)

Paul Lamar
 
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